In the combustion of a fuel, such as coal, oil, natural gas, peat, waste, etc., in a combustion plant, such as those associated with boiler systems for providing steam to a power plant, a hot process gas (or flue gas) is generated. Such a flue gas will often contain, among other things, carbon dioxide (CO2). The negative environmental effects of releasing carbon dioxide to the atmosphere have been widely recognized, and have resulted in the development of processes adapted for removing carbon dioxide from the hot process gas generated in the combustion of the above mentioned fuels.
In processes used for industrial separation of CO2, liquid solutions comprising amine compounds are commonly used as an absorbent. Examples of amine compounds commonly used in absorption of CO2 from gas streams include monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), diisopropylamine (DIPA) and aminoethoxyethanol (diglycolamine) (DGA). The most commonly used amines compounds in industrial plants are the alkanolamines MEA, DEA, and MDEA.
CO2 in the gas stream is captured in the liquid absorbent solution in an absorption process. A CO2 absorber is employed to establish suitable conditions (temperature, pressure, turbulence, etc.) for chemical absorption of CO2 into the amine absorbent from a mixed gas stream.
The amine absorbent containing absorbed CO2 is subsequently regenerated, whereby absorbed CO2 is separated from the absorbent, and the regenerated absorbent is then reused in the CO2 absorption process. Thus, a circulating absorbent stream is formed. Regeneration is generally achieved by heating the amine absorbent in a stripper reboiler to a temperature at which CO2 is released from the absorbent.
In the regenerator reboiler the absorbent is subjected to high temperature (generally about 115° C. or higher), whereas in the absorber the absorbent is exposed to higher O2 environment. As a result of the exposure to high temperature and/or the presence of O2, the amine solvent(s) of the absorbent may undergo degradation, whereby undesired degradation products are formed in the liquid phase. These degradation products, known as heat stable salts or heat stable amine salts (HSS), may accumulate in the circulating absorbent stream. The HSS reduce the CO2 removal potency of the absorbent and may therefore preferably be removed from the absorbent stream. A common method of HSS removal is to take a slipstream from the circulating absorbent, separate the bulk absorbent from the HSS in a reclaimer and recycle the separated amine back to the circulating absorbent loop as reclaimed absorbent. A relaimer can consist of a distillation, ion exchange, or electrodialysis unit.